203 research outputs found
Dynamic Base Station Repositioning to Improve Spectral Efficiency of Drone Small Cells
With recent advancements in drone technology, researchers are now considering
the possibility of deploying small cells served by base stations mounted on
flying drones. A major advantage of such drone small cells is that the
operators can quickly provide cellular services in areas of urgent demand
without having to pre-install any infrastructure. Since the base station is
attached to the drone, technically it is feasible for the base station to
dynamic reposition itself in response to the changing locations of users for
reducing the communication distance, decreasing the probability of signal
blocking, and ultimately increasing the spectral efficiency. In this paper, we
first propose distributed algorithms for autonomous control of drone movements,
and then model and analyse the spectral efficiency performance of a drone small
cell to shed new light on the fundamental benefits of dynamic repositioning. We
show that, with dynamic repositioning, the spectral efficiency of drone small
cells can be increased by nearly 100\% for realistic drone speed, height, and
user traffic model and without incurring any major increase in drone energy
consumption.Comment: Accepted at IEEE WoWMoM 2017 - 9 pages, 2 tables, 4 figure
A New Look at MIMO Capacity in the Millimeter Wave
In this paper, we present a new theoretical discovery that the multiple-input
and multiple-output (MIMO) capacity can be influenced by atmosphere molecules.
In more detail, some common atmosphere molecules, such as Oxygen and water, can
absorb and re-radiate energy in their natural resonance frequencies, such as
60GHz, 120GHz, and 180GHz, which belong to the millimeter wave (mmWave)
spectrum. Such phenomenon can provide equivalent non-line-of-sight (NLoS) paths
in an environment that lacks scatterers, and thus greatly improve the spatial
multiplexing and diversity of a MIMO system. This kind of performance
improvement is particularly useful for most mmWave communications that heavily
rely on line-of-sight (LoS) transmissions. To sum up, our study concludes that
since the molecular re-radiation happens at certain mmWave frequency bands, the
MIMO capacity becomes highly frequency selective and enjoys a considerable
boosting at those mmWave frequency bands. The impact of our new discovery is
significant, which fundamentally changes our understanding on the relationship
between the MIMO capacity and the frequency spectrum. In particular, our
results predict that several mmWave bands can serve as valuable spectrum
windows for high-efficiency MIMO communications, which in turn may shift the
paradigm of research, standardization, and implementation in the field of
mmWave communications.Comment: arXiv admin note: text overlap with arXiv:1710.0903
Enhancing Cellular Communications for UAVs via Intelligent Reflective Surface
Intelligent reflective surfaces (IRSs) capable of reconfiguring their
electromagnetic absorption and reflection properties in real-time are offering
unprecedented opportunities to enhance wireless communication experience in
challenging environments. In this paper, we analyze the potential of IRS in
enhancing cellular communications for UAVs, which currently suffers from poor
signal strength due to the down-tilt of base station antennas optimized to
serve ground users. We consider deployment of IRS on building walls, which can
be remotely configured by cellular base stations to coherently direct the
reflected radio waves towards specific UAVs in order to increase their received
signal strengths. Using the recently released 3GPP ground-to-air channel
models, we analyze the signal gains at UAVs due to the IRS deployments as a
function of UAV height as well as various IRS parameters including size,
altitude, and distance from base station. Our analysis suggests that even with
a small IRS, we can achieve significant signal gain for UAVs flying above the
cellular base station. We also find that the maximum gain can be achieved by
optimizing the location of IRS including its altitude and distance to BS.Comment: 6 pages, 6 figure
Energy Efficient Event Localization and Classification for Nano IoT
Advancements in nanotechnology promises new capabilities for Internet of
Things (IoT) to monitor extremely fine-grained events by deploying sensors as
small as a few hundred nanometers. Researchers predict that such tiny sensors
can transmit wireless data using graphene-based nano-antenna radiating in the
terahertz band (0.1-10 THz). Powering such wireless communications with
nanoscale energy supply, however, is a major challenge to overcome. In this
paper, we propose an energy efficient event monitoring framework for nano IoT
that enables nanosensors to update a remote base station about the location and
type of the detected event using only a single short pulse. Nanosensors encode
different events using different center frequencies with non overlapping half
power bandwidth over the entire terahertz band. Using uniform linear array
(ULA) antenna, the base station localizes the events by estimating the
direction of arrival of the pulse and classifies them from the center frequency
estimated by spectral centroid of the received signal. Simulation results
confirm that, from a distance of 1 meter, a 6th derivative Gaussian pulse
consuming only 1 atto Joule can achieve localization and classification
accuracies of 1.58 degree and 98.8%, respectively.Comment: 6 pages, 18 Figures, accepted for publication in IEEE GLOBECOM
Conference 201
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